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 * Copyright (c) 1994, 2012, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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package java.lang;

/**
 * Class {@code Object} is the root of the class hierarchy.
 * Every class has {@code Object} as a superclass. All objects,
 * including arrays, implement the methods of this class.
 *
 * @author unascribed
 * @see java.lang.Class
 * @since JDK1.0
 */
public class Object {

  private static native void registerNatives();

  static {
    registerNatives();
  }

  /**
   * Returns the runtime class of this {@code Object}. The returned
   * {@code Class} object is the object that is locked by {@code
   * static synchronized} methods of the represented class.
   *
   * <p><b>The actual result type is {@code Class<? extends |X|>}
   * where {@code |X|} is the erasure of the static type of the
   * expression on which {@code getClass} is called.</b> For
   * example, no cast is required in this code fragment:</p>
   *
   * <p>
   * {@code Number n = 0;                             }<br>
   * {@code Class<? extends Number> c = n.getClass(); }
   * </p>
   *
   * @return The {@code Class} object that represents the runtime class of this object.
   * @jls 15.8.2 Class Literals
   */
  public final native Class<?> getClass();

  /**
   * Returns a hash code value for the object. This method is
   * supported for the benefit of hash tables such as those provided by
   * {@link java.util.HashMap}.
   * <p>
   * The general contract of {@code hashCode} is:
   * <ul>
   * <li>Whenever it is invoked on the same object more than once during
   * an execution of a Java application, the {@code hashCode} method
   * must consistently return the same integer, provided no information
   * used in {@code equals} comparisons on the object is modified.
   * This integer need not remain consistent from one execution of an
   * application to another execution of the same application.
   * <li>If two objects are equal according to the {@code equals(Object)}
   * method, then calling the {@code hashCode} method on each of
   * the two objects must produce the same integer result.
   * <li>It is <em>not</em> required that if two objects are unequal
   * according to the {@link java.lang.Object#equals(java.lang.Object)}
   * method, then calling the {@code hashCode} method on each of the
   * two objects must produce distinct integer results.  However, the
   * programmer should be aware that producing distinct integer results
   * for unequal objects may improve the performance of hash tables.
   * </ul>
   * <p>
   * As much as is reasonably practical, the hashCode method defined by
   * class {@code Object} does return distinct integers for distinct
   * objects. (This is typically implemented by converting the internal
   * address of the object into an integer, but this implementation
   * technique is not required by the
   * Java&trade; programming language.)
   *
   * @return a hash code value for this object.
   * @see java.lang.Object#equals(java.lang.Object)
   * @see java.lang.System#identityHashCode
   */
  public native int hashCode();

  /**
   * Indicates whether some other object is "equal to" this one.
   * <p>
   * The {@code equals} method implements an equivalence relation
   * on non-null object references:
   * <ul>
   * <li>It is <i>reflexive</i>: for any non-null reference value
   * {@code x}, {@code x.equals(x)} should return
   * {@code true}.
   * <li>It is <i>symmetric</i>: for any non-null reference values
   * {@code x} and {@code y}, {@code x.equals(y)}
   * should return {@code true} if and only if
   * {@code y.equals(x)} returns {@code true}.
   * <li>It is <i>transitive</i>: for any non-null reference values
   * {@code x}, {@code y}, and {@code z}, if
   * {@code x.equals(y)} returns {@code true} and
   * {@code y.equals(z)} returns {@code true}, then
   * {@code x.equals(z)} should return {@code true}.
   * <li>It is <i>consistent</i>: for any non-null reference values
   * {@code x} and {@code y}, multiple invocations of
   * {@code x.equals(y)} consistently return {@code true}
   * or consistently return {@code false}, provided no
   * information used in {@code equals} comparisons on the
   * objects is modified.
   * <li>For any non-null reference value {@code x},
   * {@code x.equals(null)} should return {@code false}.
   * </ul>
   * <p>
   * The {@code equals} method for class {@code Object} implements
   * the most discriminating possible equivalence relation on objects;
   * that is, for any non-null reference values {@code x} and
   * {@code y}, this method returns {@code true} if and only
   * if {@code x} and {@code y} refer to the same object
   * ({@code x == y} has the value {@code true}).
   * <p>
   * Note that it is generally necessary to override the {@code hashCode}
   * method whenever this method is overridden, so as to maintain the
   * general contract for the {@code hashCode} method, which states
   * that equal objects must have equal hash codes.
   *
   * @param obj the reference object with which to compare.
   * @return {@code true} if this object is the same as the obj argument; {@code false} otherwise.
   * @see #hashCode()
   * @see java.util.HashMap
   */
  public boolean equals(Object obj) {
    return (this == obj);
  }

  /**
   * Creates and returns a copy of this object.  The precise meaning
   * of "copy" may depend on the class of the object. The general
   * intent is that, for any object {@code x}, the expression:
   * <blockquote>
   * <pre>
   * x.clone() != x</pre></blockquote>
   * will be true, and that the expression:
   * <blockquote>
   * <pre>
   * x.clone().getClass() == x.getClass()</pre></blockquote>
   * will be {@code true}, but these are not absolute requirements.
   * While it is typically the case that:
   * <blockquote>
   * <pre>
   * x.clone().equals(x)</pre></blockquote>
   * will be {@code true}, this is not an absolute requirement.
   * <p>
   * By convention, the returned object should be obtained by calling
   * {@code super.clone}.  If a class and all of its superclasses (except
   * {@code Object}) obey this convention, it will be the case that
   * {@code x.clone().getClass() == x.getClass()}.
   * <p>
   * By convention, the object returned by this method should be independent
   * of this object (which is being cloned).  To achieve this independence,
   * it may be necessary to modify one or more fields of the object returned
   * by {@code super.clone} before returning it.  Typically, this means
   * copying any mutable objects that comprise the internal "deep structure"
   * of the object being cloned and replacing the references to these
   * objects with references to the copies.  If a class contains only
   * primitive fields or references to immutable objects, then it is usually
   * the case that no fields in the object returned by {@code super.clone}
   * need to be modified.
   * <p>
   * The method {@code clone} for class {@code Object} performs a
   * specific cloning operation. First, if the class of this object does
   * not implement the interface {@code Cloneable}, then a
   * {@code CloneNotSupportedException} is thrown. Note that all arrays
   * are considered to implement the interface {@code Cloneable} and that
   * the return type of the {@code clone} method of an array type {@code T[]}
   * is {@code T[]} where T is any reference or primitive type.
   * Otherwise, this method creates a new instance of the class of this
   * object and initializes all its fields with exactly the contents of
   * the corresponding fields of this object, as if by assignment; the
   * contents of the fields are not themselves cloned. Thus, this method
   * performs a "shallow copy" of this object, not a "deep copy" operation.
   * <p>
   * The class {@code Object} does not itself implement the interface
   * {@code Cloneable}, so calling the {@code clone} method on an object
   * whose class is {@code Object} will result in throwing an
   * exception at run time.
   *
   * @return a clone of this instance.
   * @throws CloneNotSupportedException if the object's class does not support the {@code Cloneable}
   * interface. Subclasses that override the {@code clone} method can also throw this exception to
   * indicate that an instance cannot be cloned.
   * @see java.lang.Cloneable
   */
  protected native Object clone() throws CloneNotSupportedException;

  /**
   * Returns a string representation of the object. In general, the
   * {@code toString} method returns a string that
   * "textually represents" this object. The result should
   * be a concise but informative representation that is easy for a
   * person to read.
   * It is recommended that all subclasses override this method.
   * <p>
   * The {@code toString} method for class {@code Object}
   * returns a string consisting of the name of the class of which the
   * object is an instance, the at-sign character `{@code @}', and
   * the unsigned hexadecimal representation of the hash code of the
   * object. In other words, this method returns a string equal to the
   * value of:
   * <blockquote>
   * <pre>
   * getClass().getName() + '@' + Integer.toHexString(hashCode())
   * </pre></blockquote>
   *
   * @return a string representation of the object.
   */
  public String toString() {
    return getClass().getName() + "@" + Integer.toHexString(hashCode());
  }

  /**
   * Wakes up a single thread that is waiting on this object's
   * monitor. If any threads are waiting on this object, one of them
   * is chosen to be awakened. The choice is arbitrary and occurs at
   * the discretion of the implementation. A thread waits on an object's
   * monitor by calling one of the {@code wait} methods.
   * <p>
   * The awakened thread will not be able to proceed until the current
   * thread relinquishes the lock on this object. The awakened thread will
   * compete in the usual manner with any other threads that might be
   * actively competing to synchronize on this object; for example, the
   * awakened thread enjoys no reliable privilege or disadvantage in being
   * the next thread to lock this object.
   * <p>
   * This method should only be called by a thread that is the owner
   * of this object's monitor. A thread becomes the owner of the
   * object's monitor in one of three ways:
   * <ul>
   * <li>By executing a synchronized instance method of that object.
   * <li>By executing the body of a {@code synchronized} statement
   * that synchronizes on the object.
   * <li>For objects of type {@code Class,} by executing a
   * synchronized static method of that class.
   * </ul>
   * <p>
   * Only one thread at a time can own an object's monitor.
   *
   * @throws IllegalMonitorStateException if the current thread is not the owner of this object's
   * monitor.
   * @see java.lang.Object#notifyAll()
   * @see java.lang.Object#wait()
   */
  public final native void notify();

  /**
   * Wakes up all threads that are waiting on this object's monitor. A
   * thread waits on an object's monitor by calling one of the
   * {@code wait} methods.
   * <p>
   * The awakened threads will not be able to proceed until the current
   * thread relinquishes the lock on this object. The awakened threads
   * will compete in the usual manner with any other threads that might
   * be actively competing to synchronize on this object; for example,
   * the awakened threads enjoy no reliable privilege or disadvantage in
   * being the next thread to lock this object.
   * <p>
   * This method should only be called by a thread that is the owner
   * of this object's monitor. See the {@code notify} method for a
   * description of the ways in which a thread can become the owner of
   * a monitor.
   *
   * @throws IllegalMonitorStateException if the current thread is not the owner of this object's
   * monitor.
   * @see java.lang.Object#notify()
   * @see java.lang.Object#wait()
   */
  public final native void notifyAll();

  /**
   * Causes the current thread to wait until either another thread invokes the
   * {@link java.lang.Object#notify()} method or the
   * {@link java.lang.Object#notifyAll()} method for this object, or a
   * specified amount of time has elapsed.
   * <p>
   * The current thread must own this object's monitor.
   * <p>
   * This method causes the current thread (call it <var>T</var>) to
   * place itself in the wait set for this object and then to relinquish
   * any and all synchronization claims on this object. Thread <var>T</var>
   * becomes disabled for thread scheduling purposes and lies dormant
   * until one of four things happens:
   * <ul>
   * <li>Some other thread invokes the {@code notify} method for this
   * object and thread <var>T</var> happens to be arbitrarily chosen as
   * the thread to be awakened.
   * <li>Some other thread invokes the {@code notifyAll} method for this
   * object.
   * <li>Some other thread {@linkplain Thread#interrupt() interrupts}
   * thread <var>T</var>.
   * <li>The specified amount of real time has elapsed, more or less.  If
   * {@code timeout} is zero, however, then real time is not taken into
   * consideration and the thread simply waits until notified.
   * </ul>
   * The thread <var>T</var> is then removed from the wait set for this
   * object and re-enabled for thread scheduling. It then competes in the
   * usual manner with other threads for the right to synchronize on the
   * object; once it has gained control of the object, all its
   * synchronization claims on the object are restored to the status quo
   * ante - that is, to the situation as of the time that the {@code wait}
   * method was invoked. Thread <var>T</var> then returns from the
   * invocation of the {@code wait} method. Thus, on return from the
   * {@code wait} method, the synchronization state of the object and of
   * thread {@code T} is exactly as it was when the {@code wait} method
   * was invoked.
   * <p>
   * A thread can also wake up without being notified, interrupted, or
   * timing out, a so-called <i>spurious wakeup</i>.  While this will rarely
   * occur in practice, applications must guard against it by testing for
   * the condition that should have caused the thread to be awakened, and
   * continuing to wait if the condition is not satisfied.  In other words,
   * waits should always occur in loops, like this one:
   * <pre>
   *     synchronized (obj) {
   *         while (&lt;condition does not hold&gt;)
   *             obj.wait(timeout);
   *         ... // Perform action appropriate to condition
   *     }
   * </pre>
   * (For more information on this topic, see Section 3.2.3 in Doug Lea's
   * "Concurrent Programming in Java (Second Edition)" (Addison-Wesley,
   * 2000), or Item 50 in Joshua Bloch's "Effective Java Programming
   * Language Guide" (Addison-Wesley, 2001).
   *
   * <p>If the current thread is {@linkplain java.lang.Thread#interrupt()
   * interrupted} by any thread before or while it is waiting, then an
   * {@code InterruptedException} is thrown.  This exception is not
   * thrown until the lock status of this object has been restored as
   * described above.
   *
   * <p>
   * Note that the {@code wait} method, as it places the current thread
   * into the wait set for this object, unlocks only this object; any
   * other objects on which the current thread may be synchronized remain
   * locked while the thread waits.
   * <p>
   * This method should only be called by a thread that is the owner
   * of this object's monitor. See the {@code notify} method for a
   * description of the ways in which a thread can become the owner of
   * a monitor.
   *
   * @param timeout the maximum time to wait in milliseconds.
   * @throws IllegalArgumentException if the value of timeout is negative.
   * @throws IllegalMonitorStateException if the current thread is not the owner of the object's
   * monitor.
   * @throws InterruptedException if any thread interrupted the current thread before or while the
   * current thread was waiting for a notification.  The <i>interrupted status</i> of the current
   * thread is cleared when this exception is thrown.
   * @see java.lang.Object#notify()
   * @see java.lang.Object#notifyAll()
   */
  public final native void wait(long timeout) throws InterruptedException;

  /**
   * Causes the current thread to wait until another thread invokes the
   * {@link java.lang.Object#notify()} method or the
   * {@link java.lang.Object#notifyAll()} method for this object, or
   * some other thread interrupts the current thread, or a certain
   * amount of real time has elapsed.
   * <p>
   * This method is similar to the {@code wait} method of one
   * argument, but it allows finer control over the amount of time to
   * wait for a notification before giving up. The amount of real time,
   * measured in nanoseconds, is given by:
   * <blockquote>
   * <pre>
   * 1000000*timeout+nanos</pre></blockquote>
   * <p>
   * In all other respects, this method does the same thing as the
   * method {@link #wait(long)} of one argument. In particular,
   * {@code wait(0, 0)} means the same thing as {@code wait(0)}.
   * <p>
   * The current thread must own this object's monitor. The thread
   * releases ownership of this monitor and waits until either of the
   * following two conditions has occurred:
   * <ul>
   * <li>Another thread notifies threads waiting on this object's monitor
   * to wake up either through a call to the {@code notify} method
   * or the {@code notifyAll} method.
   * <li>The timeout period, specified by {@code timeout}
   * milliseconds plus {@code nanos} nanoseconds arguments, has
   * elapsed.
   * </ul>
   * <p>
   * The thread then waits until it can re-obtain ownership of the
   * monitor and resumes execution.
   * <p>
   * As in the one argument version, interrupts and spurious wakeups are
   * possible, and this method should always be used in a loop:
   * <pre>
   *     synchronized (obj) {
   *         while (&lt;condition does not hold&gt;)
   *             obj.wait(timeout, nanos);
   *         ... // Perform action appropriate to condition
   *     }
   * </pre>
   * This method should only be called by a thread that is the owner
   * of this object's monitor. See the {@code notify} method for a
   * description of the ways in which a thread can become the owner of
   * a monitor.
   *
   * @param timeout the maximum time to wait in milliseconds.
   * @param nanos additional time, in nanoseconds range 0-999999.
   * @throws IllegalArgumentException if the value of timeout is negative or the value of nanos is
   * not in the range 0-999999.
   * @throws IllegalMonitorStateException if the current thread is not the owner of this object's
   * monitor.
   * @throws InterruptedException if any thread interrupted the current thread before or while the
   * current thread was waiting for a notification.  The <i>interrupted status</i> of the current
   * thread is cleared when this exception is thrown.
   */
  public final void wait(long timeout, int nanos) throws InterruptedException {
    if (timeout < 0) {
      throw new IllegalArgumentException("timeout value is negative");
    }

    if (nanos < 0 || nanos > 999999) {
      throw new IllegalArgumentException(
          "nanosecond timeout value out of range");
    }

    if (nanos > 0) {
      timeout++;
    }

    wait(timeout);
  }

  /**
   * Causes the current thread to wait until another thread invokes the
   * {@link java.lang.Object#notify()} method or the
   * {@link java.lang.Object#notifyAll()} method for this object.
   * In other words, this method behaves exactly as if it simply
   * performs the call {@code wait(0)}.
   * <p>
   * The current thread must own this object's monitor. The thread
   * releases ownership of this monitor and waits until another thread
   * notifies threads waiting on this object's monitor to wake up
   * either through a call to the {@code notify} method or the
   * {@code notifyAll} method. The thread then waits until it can
   * re-obtain ownership of the monitor and resumes execution.
   * <p>
   * As in the one argument version, interrupts and spurious wakeups are
   * possible, and this method should always be used in a loop:
   * <pre>
   *     synchronized (obj) {
   *         while (&lt;condition does not hold&gt;)
   *             obj.wait();
   *         ... // Perform action appropriate to condition
   *     }
   * </pre>
   * This method should only be called by a thread that is the owner
   * of this object's monitor. See the {@code notify} method for a
   * description of the ways in which a thread can become the owner of
   * a monitor.
   *
   * @throws IllegalMonitorStateException if the current thread is not the owner of the object's
   * monitor.
   * @throws InterruptedException if any thread interrupted the current thread before or while the
   * current thread was waiting for a notification.  The <i>interrupted status</i> of the current
   * thread is cleared when this exception is thrown.
   * @see java.lang.Object#notify()
   * @see java.lang.Object#notifyAll()
   */
  public final void wait() throws InterruptedException {
    wait(0);
  }

  /**
   * Called by the garbage collector on an object when garbage collection
   * determines that there are no more references to the object.
   * A subclass overrides the {@code finalize} method to dispose of
   * system resources or to perform other cleanup.
   * <p>
   * The general contract of {@code finalize} is that it is invoked
   * if and when the Java&trade; virtual
   * machine has determined that there is no longer any
   * means by which this object can be accessed by any thread that has
   * not yet died, except as a result of an action taken by the
   * finalization of some other object or class which is ready to be
   * finalized. The {@code finalize} method may take any action, including
   * making this object available again to other threads; the usual purpose
   * of {@code finalize}, however, is to perform cleanup actions before
   * the object is irrevocably discarded. For example, the finalize method
   * for an object that represents an input/output connection might perform
   * explicit I/O transactions to break the connection before the object is
   * permanently discarded.
   * <p>
   * The {@code finalize} method of class {@code Object} performs no
   * special action; it simply returns normally. Subclasses of
   * {@code Object} may override this definition.
   * <p>
   * The Java programming language does not guarantee which thread will
   * invoke the {@code finalize} method for any given object. It is
   * guaranteed, however, that the thread that invokes finalize will not
   * be holding any user-visible synchronization locks when finalize is
   * invoked. If an uncaught exception is thrown by the finalize method,
   * the exception is ignored and finalization of that object terminates.
   * <p>
   * After the {@code finalize} method has been invoked for an object, no
   * further action is taken until the Java virtual machine has again
   * determined that there is no longer any means by which this object can
   * be accessed by any thread that has not yet died, including possible
   * actions by other objects or classes which are ready to be finalized,
   * at which point the object may be discarded.
   * <p>
   * The {@code finalize} method is never invoked more than once by a Java
   * virtual machine for any given object.
   * <p>
   * Any exception thrown by the {@code finalize} method causes
   * the finalization of this object to be halted, but is otherwise
   * ignored.
   *
   * @throws Throwable the {@code Exception} raised by this method
   * @jls 12.6 Finalization of Class Instances
   * @see java.lang.ref.WeakReference
   * @see java.lang.ref.PhantomReference
   */
  protected void finalize() throws Throwable {
  }
}
